[fyleow]

I'm going to be building my META42 soon and here is my parts list.

Current Source: Nomade Jukebox 3 --> CMOY --> Sennheiser HD 580

POT - Panasonic 10.5k (Max resistance)
R1 - 1k
R2 - 105k
R3 - 470
R4 - 4.7K
R5 - 10k
R6 - 1M
R7 - 100
R8 - None
R9 - None
R10 - 100

C1 - "Alt. 1.0 ìF 100V+ metalized polypropylene film capacitor"
C2 and 3 (4X) - "1000 ìF 10V 16mm tall long-life electrolytic capacitor, radial"
C4 - "Alt. 1.0 ìF 63V metalized polyester box cap"
C5 - None

D1 diode will be included
4 JFET Transistors included

Power Supply - Mouser part # 412112103
HI-Q AC Adaptor 12V DC 1 AMP

Just need to check some stuff.

My R3 to R6 resistors are actually taken from a thread at Headwize (META42 Success) and I plugged it into Tangent's calculator and it says that has a Gain of about 10. Since I'm using the OPA637 the higher Gain will be more stable.

A quick PSU question. What AMP is best for the META42? I notice there are a bunch of different ratings for 12VDC adaptors. Will the one I picked work well? I can just wire it directly into the V+ and V- spots on the META42 right? No special things in between needed?

Anyone have suggestions on changes before I place my order?

Thanks.

 

[andrzejpw]

Hmm, wondering one thing. . .

Why are you only getting a 12V psu? Isn't the meta made for 18v?

Note: I'm very stupid when it comes to DIY.

 

[fyleow]

You can't be as clueless as me when it comes to DIY!

12V was the highest I saw on the Mouser catalog, the next jump is 24V. The META42 works with 9V to 24V depending on Opamp I think.

 

[fyleow]

Seems like the power supply is unregulated, that would be a problem right?

 

[Nezer]

Quote:

Originally posted by fyleow You can't be as clueless as me when it comes to DIY! 12V was the highest I saw on the Mouser catalog, the next jump is 24V. The META42 works with 9V to 24V depending on Opamp I think.

Teh board doesn't care about the voltage (until you get to really high voltages or really, really low voltages), only the components.

With the OPA637 you are probably going to want to use the 24V supply which will provide +/- 12V to the opamp and buffers. Running a 12V supply will only provide 6Vs on the rails and the 637 probably isn't going to care for this too much (I'll have to look at the datasheet, it will probably work but may adversly effect the sound).

Try your best and get a linear regulated, non-switching power supply. An unregulated supply will vary the voltage quite a bit and you will have to account for that when specing your parts.

I would *seriously* consider nothing less than 35V caps for C2 and C3. 10V is going to be quite weak and will limit you to 20V input max and you risk blowing the caps if the rails are shorted. Stepping up to 35V will cost you in capacitance but will save you in case of a mistake or a higher voltage supply that I really think you're going to need.

Another idea is to socket *Everything*, caps included. This makes it easy to change parts and tweak as much as desired.

I have made the following calculations with regards to sockets for as many things as possible:

4 x 8-pin DIP gold-plated socket
6 x 7 position SIP socket, gold-plated, single row
2 x 5 position SIP socket, gold-plated, single row
5 x 3 position SIP socket, gold-plated, single row
11 x 2 position SIP socket, gold-plated, single row
14 x 1 position SIP socket, gold-plated, single row


This will socket everything but the pot and make tweaking and playing a non-soldering event. If you got an Alps Blue you could probably socket it too with 6 more 1 position SIP sockets.

At a minimum socket the opamp folowed by the buffers follwed by the resistors.

I also suggest picking-up the buffers (get 6 and stack) as well as the C4 caps from Tangent when you order.

If using a multiloop topology having a gain of 10 in the circuit for the 637 isn't necessarry as the R5/R6 gain determines what the opamp sees. For the 637 calculate a gain of around 800 to limit bandwidth to around 100kHz. If using his calculator for this set the tolerance pretty high. You should fine a few options around a G of 790-791.

I would also consider talking to Erix about some Cerafine caps for this project. I just got my board today and have yet to see which Cerafines will fit but the 220s probably will with ease and the 470s MIGHT with a little coaxing. I personally would take a 470uF Cerafine over a generic 1000uF anyday.

Also, with the 637, consider using the EL2002s as the follower instead of the 2001s. A high-bandwidth opamp deserves a high-bandwidth follower.

I'm personally planning on stacking 2 2002s per channel and 3 2001s on the power supply buffer. I don;t know what I'll gain but I'm not going to lose anything and it will look pretty cool.

 

[erix]

I've yet to build one of these but it seems to me your C2 & C3 caps voltage rating is too low. Assuming you are getting nothing but 12V out of your adapter, you will have +6V going through two of the caps and -6V through the other.

What happens if, for some reason, the voltage splitter doesn't split and lets all 12V go through your caps? Poof - out comes the magic smoke (well probably not smoke - just poof). So you should have caps rated for at least 12V.

Now, the cold reality of low-cost power supplies (wall warts) are that they put out much more than their rated voltage under a light load. They are supposed to provide 12V at 1A, or whatever the amp rating is. But at loads less than 1A You may be getting 15V or more out of that thing. The META amp, being designed primarily as a portable, is very battery friendly, meaning it doesn't draw much current, probably less than 100mA at ludicrous volume with stacked buffers and a bright LED. It's a safe bet that this PS will provide more than 12V, how much can only be determined when it's plugged in and running.

I would use no less than 16V rated caps for a 12V wall wart-powered amp.

ok,
erix

 

[fyleow]

Ok it looks like there is WAY too many problems with using a Wall Wart. I'm too cheap to spend the cash on a regulated power supply so I might just go with batteries. I'm going to be using 24V I guess then? Wouldn't that mean alot of AA batteries though? heh.

Which means my caps have to be able to take at least 12V on each side. I guess the "Alt. 1000 ìF 25V 30mm tall" will work then?

About socketing everything and adding extra buffers I will have to check the cost of all those out. It does sound cool though since I can customize it whenever and however I want.

About the 10 Gain, I can keep it at this if I wanted to right? I don't want to make things too complicated....

 

[puppyslugg]

I agree with nezer/erix: using caps rated for 16v or higher will give more options as to which psu can be used. The opamps may perform better with more voltage. Personally, I prefer, as nezer, a regulated linear psu.

BTW: is the META going to be used as a portable unit or staionary one?

 

[fyleow]

I'm going to be using it as stationary only.

 

[Nezer]

Quote:

Originally posted by fyleow Ok it looks like there is WAY too many problems with using a Wall Wart. I'm too cheap to spend the cash on a regulated power supply so I might just go with batteries. I'm going to be using 24V I guess then? Wouldn't that mean alot of AA batteries though? heh. Which means my caps have to be able to take at least 12V on each side. I guess the "Alt. 1000 ìF 25V 30mm tall" will work then? About socketing everything and adding extra buffers I will have to check the cost of all those out. It does sound cool though since I can customize it whenever and however I want. About the 10 Gain, I can keep it at this if I wanted to right? I don't want to make things too complicated....

The cost of socketing everything is about $30 from Digi-key.

Sure, you can set whatever gain you want!

As for the power supply. A liner regulated supply is going to be a LOT cheaper in the long run over AAs!!

As for the cap, they only consideration you have to give height is whatever case you are going to put it in. Also, the 1000uF isn't a set number. The only real consideration to size you have to give from the boards perspective is the diameter of the caps. If I had to eyball it I'd say these are 10mm placements, but I'm an american so I can't eyeball metric worth a crap.

 

[fyleow]

If that is the case I will probably going to be using the 330uF 25V 12.5mm then. I will be using 4 of them so it shouldn't be a problem. Even if I use rechargable batteries the cost will still be high?

 

[fyleow]

Looks like if I go the AA route I will need ALOT of batteries. Ok back to power supplies

Will this one work? Mouser # 552-PSC-15A-240S

15 Watt Wall Plug In Adapter
24 V DC 0.63 A
I think it's regulated, it says "Regulation +/- 5%"

 

[puppyslugg]

Quote:

I'm going to be using it as stationary only.

Then you won't need the battery circuitry, (vritual ground driver, splitter, etc.), but you will need a bipolar psu. I know you want to keep simple as possible, but seriously consider a linear reg. psu. I believe it will extract more out of the meta. After all the trouble and effort in buliding a meta, you really don't want to cheese out on the psu, IMO.

 

[fyleow]

Ok well will the one I listed work? How do I check if it's bipolar or not? It doesn't say.

 

[tangent]

Quote:

I think it's regulated, it says "Regulation +/- 5%"

There are two kinds of regulated power supplies. See this article for more info on this, especially as it applies to op-amp based amplifiers:

http://tangentsoft.net/audio/opamp-ps.html

The noise calcuation math is wrong, by the way, but the basic premise of the article stands. I'll be correcting the article Real Soon Now.

Anyway, if you want a linear regulated power supply, that Phihong unit isn't it. The biggest name in affordable linear-regulated wall warts is Elpac's WM series. (Not to be confused with the MW series or the W series.) DigiKey, Allied and Newark all carry subsets of the Elpac WM line. Personally, I'm a fan of the WM080.

You can get a good linear regulated power supply for around $30. If you buy AA batteries in bulk, they're about 90 cents apiece -- you'd only have to buy 34 of them before a $30 power supply paid for itself! Let's say you're getting 100 hours of run time from a set of 18 batteries (a reasonable AA battery pack, and a reasonable run time for such a pack), and you listen for 6 hours a week. You would break even after 33 weeks -- barely over half a year!

Quote:

Then you won't need the battery circuitry, (vritual ground driver, splitter, etc.), but you will need a bipolar psu.

Remember, we're dealing with a guy here who's complaining about spending $30 on a power supply. Dual-voltage linears cost about twice as much as single-voltage linears. It's cheaper to just stick with the rail splitter/buffer than to get a better power supply. I'll grant that a true dual voltage supply is better, but ask yourself what the likelihood is that you'll convince Mr. Slugg of that?

(For multi-voltage, I'm a fan of the WM113TT, for what that's worth -- it's a triple output supply, but it's worth using it as a dual because it's a tabletop model -- cords coming out each side, as opposed to a true wall wart.)